1. Field of the Invention
The present invention relates to a semiconductor laser device, and more particularly to a so-called broad area semiconductor laser device.
2. Background Art
Broad area semiconductor laser devices have an advantage, among others, that they can produce high output power. Conventional broad area semiconductor laser devices have an electrode stripe structure having a width of 50 μm or 160 μm, as disclosed, e.g., in K. Honda, T. Mamine, and M. Ayabe, “Single stripe high power laser diodes made by Metal-Organic Chemical Vapor Deposition,” SPIE, Vol. 893, High Power Laser Diodes and Applications, pp. 16-20, 1988.
Further, semiconductor lasers with a stripe structure which are not broad area semiconductor laser devices are disclosed in Japanese Laid-Open Patent Publications Nos. H01-183603, H02-264488, 2003-060303, and 2005-072488.
The above Japanese Laid-Open Patent Publication No. H01-183603 discloses a structure in which high order mode cutoff regions are provided on both sides of a tapered core region, with cladding regions being interposed between the tapered core region and the high order mode cutoff regions. The width of the core region described in this publication is narrow at one end so that only the fundamental mode of oscillation can occur or develop therein.
Thus, this semiconductor laser device has a different structure than broad area semiconductor laser devices and hence cannot produce high output power. It should be noted that, as shown in FIG. 4 of this publication, the semiconductor laser device has a structure having a refractive index distribution and a propagation coefficient for each mode so that only the fundamental mode of oscillation can occur therein and all higher order modes are prevented from occurring.
The semiconductor laser device disclosed in the above Japanese Laid-Open Patent Publication No. H02-264488 also has a narrow stripe region in which only the fundamental mode of oscillation can occur. Therefore, unlike broad area semiconductor laser devices, this semiconductor laser device cannot produce high output power.
According to this publication, the stripe of the semiconductor laser device has a narrowed portion which prevents all modes other than the fundamental mode from occurring; that is, this semiconductor laser device is a semiconductor laser having a resonator structure in which only the fundamental mode of oscillation can occur and all higher order modes are prevented from occurring.
The above Japanese Laid-Open Patent Publication Nos. 2003-060303 and 2005-072488 also disclose single mode semiconductor laser devices, not broad area semiconductor laser devices.
Broad area semiconductor laser devices tend to have a large horizontal beam divergence angle, typically in the range of approximately 10-13 degrees. This large beam divergence angle results in a decrease in the brightness of the light emitted from the broad area semiconductor laser device.